Up-regulation of sodium channel subunit mRNAs and their cell surface expression by antiepileptic valproic acid: activation of calcium channel and catecholamine secretion in adrenal chromaffin cells

Reviewing Evidence for the Relationship of EEG Abnormalities and RTT Phenotype Paralleled by Insights from Animal Studies

Rett syndrome (RTT) is a rare neurodevelopmental disorder that is usually caused by mutations of the MECP2 gene. Patients with RTT suffer from severe deficits in motor, perceptual and cognitive domains. Electroencephalogram (EEG) has provided useful information to clinicians and scientists, from the very first descriptions of RTT, and yet no reliable neurophysiological biomarkers related to the pathophysiology of the disorder or symptom severity have been identified to date. To identify consistently observed and potentially informative EEG characteristics of RTT pathophysiology, and ascertain areas most worthy of further systematic investigation, here we review the literature for EEG abnormalities reported in patients with RTT and in its disease models. While pointing to some promising potential EEG biomarkers of RTT, our review identify areas of need to realize the potential of EEG including (1) quantitative investigation of promising clinical-EEG observations in RTT, e.g., shift of mu rhythm frequency and EEG during sleep; (2) closer alignment of approaches between patients with RTT and its animal models to strengthen the translational significance of the work (e.g., EEG measurements and behavioral states); (3) establishment of large-scale consortium research, to provide adequate Ns to investigate age and genotype effects.

Spider Knottin Pharmacology at Voltage-Gated Sodium Channels and Their Potential to Modulate Pain Pathways

Voltage-gated sodium channels (Na_Vs) are a key determinant of neuronal signalling. Neurotoxins from diverse taxa that selectively activate or inhibit Na_V channels have helped unravel the role of Na_V channels in diseases, including chronic pain. Spider venoms contain the most diverse array of inhibitor cystine knot (ICK) toxins (knottins). This review provides an overview on how spider knottins modulate Na_V channels and describes the structural features and molecular determinants that influence their affinity and subtype selectivity. Genetic and functional evidence support a major involvement of Na_V subtypes in various chronic pain conditions. The exquisite inhibitory properties of spider knottins over key Na_V subtypes make them the best lead molecules for the development of novel analgesics to treat chronic pain.

Acquired cardiac channelopathies in epilepsy: Evidence, mechanisms, and clinical significance

There is growing evidence that cardiac dysfunction in patients with chronic epilepsy could play a pathogenic role in sudden unexpected death in epilepsy (SUDEP). Recent animal studies have revealed that epilepsy secondarily alters the expression of cardiac ion channels alongside abnormal cardiac electrophysiology and remodeling. These molecular findings represent novel evidence for an acquired cardiac channelopathy in epilepsy, distinct from inherited ion channels mutations associated with cardiocerebral phenotypes. Specifically, seizure activity has been shown to alter the messenger RNA (mRNA) and protein expression of voltage-gated sodium channels (Na_v 1.1, Na_v 1.5), voltage-gated potassium channels (K_v 4.2, K_v 4.3), sodium-calcium exchangers (NCX1), and nonspecific cation-conducting channels (HCN2, HCN4). The pathophysiology may involve autonomic dysfunction and structural cardiac disease, as both are independently associated with epilepsy and ion channel dysregulation. Indeed, in vivo and in vitro studies of cardiac pathology reveal a complex network of signaling pathways and transcription factors regulating ion channel expression in the setting of sympathetic overactivity, cardiac failure, and hypertrophy. Other mechanisms such as circulating inflammatory mediators or exogenous effects of antiepileptic medications lack evidence. Moreover, an acquired cardiac channelopathy may underlie the electrophysiologic cardiac abnormalities seen in chronic epilepsy, potentially contributing to the increased risk of malignant arrhythmias and sudden death. Therefore, further investigation is necessary to establish whether cardiac ion channel dysregulation similarly occurs in patients with epilepsy, and to characterize any pathogenic relationship with SUDEP.

Sodium channels and pain: from toxins to therapies

Voltage-gated sodium channels (NaV channels) are essential for the initiation and propagation of action potentials that critically influence our ability to respond to a diverse range of stimuli. Physiological and pharmacological studies have linked abnormal function of NaV channels to many human disorders, including chronic neuropathic pain. These findings, along with the description of the functional properties and expression pattern of NaV channel subtypes, are helping to uncover subtype specific roles in acute and chronic pain and revealing potential opportunities to target these with selective inhibitors. High-throughput screens and automated electrophysiology platforms have identified natural toxins as a promising group of molecules for the development of target-specific analgesics. In this review, the role of toxins in defining the contribution of NaV channels in acute and chronic pain states and their potential to be used as analgesic therapies are discussed.

LINKED ARTICLES

This article is part of a themed section on Recent Advances in Targeting Ion Channels to Treat Chronic Pain. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.12/issuetoc.

The role of REST and HDAC2 in epigenetic dysregulation of Nav1.5 and nNav1.5 expression in breast cancer

BACKGROUND

Increased expression of voltage-gated sodium channels (VGSCs) have been implicated with strong metastatic potential of human breast cancer in vitro and in vivo where the main culprits are cardiac isoform Nav1.5 and its 'neonatal' splice variant, nNav1.5. Several factors have been associated with Nav1.5 and nNav1.5 gain of expression in breast cancer mainly hormones, and growth factors.

AIM

This study aimed to investigate the role of epigenetics via transcription repressor, repressor element silencing transcription factor (REST) and histone deacetylases (HDACs) in enhancing Nav1.5 and nNav1.5 expression in human breast cancer by assessing the effect of HDAC inhibitor, trichostatin A (TSA).

METHODS

The less aggressive human breast cancer cell line, MCF-7 cells which lack Nav1.5 and nNav1.5 expression was treated with TSA at a concentration range 10-10,000 ng/ml for 24 h whilst the aggressive MDA-MB-231 cells was used as control. The effect of TSA on Nav1.5, nNav1.5, REST, HDAC1, HDAC2, HDAC3, MMP2 and N-cadherin gene expression level was analysed by real-time PCR. Cell growth (MTT assay) and metastatic behaviors (lateral motility and migration assays) were also measured.

RESULTS

mRNA expression level of Nav1.5 and nNav1.5 were initially very low in MCF-7 compared to MDA-MB-231 cells. Inversely, mRNA expression level of REST, HDAC1, HDAC2, and HDAC3 were all greater in MCF-7 compared to MDA-MB-231 cells. Treatment with TSA significantly increased the mRNA expression level of Nav1.5 and nNav1.5 in MCF-7 cells. On the contrary, TSA significantly reduced the mRNA expression level of REST and HDAC2 in this cell line. Remarkably, despite cell growth inhibition by TSA, motility and migration of MCF-7 cells were enhanced after TSA treatment, confirmed with the up-regulation of metastatic markers, MMP2 and N-cadherin.

CONCLUSIONS

This study identified epigenetics as another factor that regulate the expression level of Nav1.5 and nNav1.5 in breast cancer where REST and HDAC2 play important role as epigenetic regulators that when lacking enhances the expression of Nav1.5 and nNav1.5 thus promotes motility and migration of breast cancer. Elucidation of the regulatory mechanisms for gain of Nav1.5 and nNav1.5 expression may be helpful for seeking effective strategies for the management of metastatic diseases.

Valproate improves memory deficits in an Alzheimer's disease mouse model: investigation of possible mechanisms of action

Alzheimer's disease (AD) is a very common progressive neurodegenerative disorder affecting the learning and memory abilities in the brain. Key findings from recent studies of epigenetic mechanisms of memory suggest chromatin remodeling disorders via histone hypoacetylation of the lysine residue contribute to the cognitive impairment in AD. Therefore, the deinhibition of histone acetylation induced by histone deacetylases (HDACs) inhibitors contributes to recovery of learning and memory. We show here that the antiepileptic drug sodium valproate (VPA) potently enhanced long-term recognition memory and spatial learning and memory in AD transgenic mice. Possible mechanisms showed VPA could significantly elevate histone acetylation through HDACs activity inhibition and increase plasticity-associated gene expression within the hippocampi of mice. Our study suggests that VPA, serving as a HDACs inhibitor, can be considered as a potential pharmaceutical agent for the improvement of cognitive function in AD.

The role of the entorhinal cortex in epileptiform activities of the hippocampus

BACKGROUND

Temporal lobe epilepsy (TLE) is the commonest type of epilepsy in adults, and the hippocampus is indicated to have a close relationship with TLE. Recent researches also indicate that the entorhinal cortex (EC) is involved in epilepsy. To explore the essential role that the EC may play in epilepsy, a computational model of the hippocampal CA3 region was built, which consisted of pyramidal cells and two types of interneurons. By changing the input signals from the EC, the effects of EC on epileptiform activities of the hippocampus were investigated. Additionally, recent studies have found that the antiepileptic drug valproate (VPA) can block ictal discharges but cannot block interictal discharges in vitro, and the mechanism under this phenomenon is still confusing. In our model, the effects of VPA on epileptiform activities were simulated and some mechanisms were explored.

RESULTS

Interictal discharges were induced in the model without the input signals from the EC, whereas the model with the EC input produced ictal discharges when the EC input contained ictal discharges. The GABA-ergic connection strength was enhanced and the NMDA-ergic connection strength was reduced to simulate the effects of VPA, and the simulation results showed that the disappearance of ictal discharges in the model mainly due to the disappearance of ictal discharges in the input signals from the EC.

CONCLUSIONS

Simulation results showed that ictal discharges in the EC were necessary for the hippocampus to generate ictal discharges, and VPA might block the ictal discharges in the EC, which led to the disappearance of ictal discharges in the hippocampus.

Endothelin-1-induced down-regulation of NaV1.7 expression in adrenal chromaffin cells: attenuation of catecholamine secretion and tau dephosphorylation

Endothelin-1 and voltage-dependent sodium channels are involved in control and suppression of neuropathological factors, which contribute to sculpting the neuronal network. We previously demonstrated that veratridine-induced NaV1.7 sodium channel activation caused intracellular calcium elevation, catecholamine secretion and tau dephosphorylation in adrenal chromaffin cells. The aim of this study was to examine whether endothelin-1 could modulate NaV1.7. Our results indicated that endothelin-1 decreased the protein level of NaV1.7 and the veratridine-induced increase in intracellular calcium. In addition, it also abolished the veratridine-induced dephosphorylation of tau and the phosphorylation of glycogen synthase kinase-3β and extracellular signal-regulated kinase. These findings suggest that the endothelin-1-induced down-regulation of NaV1.7 diminishes NaV1.7-related catecholamine secretion and dephosphorylation of tau.

Valproic acid increases white matter repair and neurogenesis after stroke

Acute treatment of stroke with histone deacetylase (HDAC) inhibitors has been shown to reduce ischemic cell damage; however, it is unclear whether delayed treatment with HDAC inhibitors will contribute to the brain repair and plasticity. In the present study, we investigated the effects of delayed treatment of stroke with a pan HDAC inhibitor, valproic acid (VPA), on white matter injury and neurogenesis during stroke recovery. Administration of VPA at a dose of 100mg/kg for 7 days starting 24h after middle cerebral artery occlusion (MCAo) in rats significantly improved neurological outcome measured 7-28 days post-MCAo. In addition, the VPA treatment significantly increased oligodendrocyte survival and newly generated oligodendrocytes, which was associated with elevation of myelinated axonal density in the ischemic boundary 28 days after MCAo. VPA treatment also increased the expression of glutamate transporter 1 (GLT1) in the ischemic boundary after stroke, and increased acetylated histone H4 expression in neuroblasts and the number of new neurons in striatal ischemic boundary region. This study provides new evidence that the delayed VPA treatment enhances white matter repair and neurogenesis in ischemic brain, which may contribute to improved functional outcome.

Insulin-induced neurite-like process outgrowth: acceleration of tau protein synthesis via a phosphoinositide 3-kinase~mammalian target of rapamycin pathway

Both insulin and tau, promoting neuronal differentiation (neurite outgrowth, neuronal polarity, and myelination) and cell survival, are associated with neurodegenerative disease (e.g., Alzheimer's disease). The aim of this study was to explore relation between insulin-induced activation of insulin signal and expression of tau protein on neurite-like process outgrowth in adrenal chromaffin cells. Primary cultured bovine adrenal chromaffin cells were incubated with insulin to determine whether stimulant of insulin signal could affect tau expression and neurite-like process outgrowth. Chronic treatment with insulin (⩾6h) led neurite-like process outgrowth as well as increased tau protein level by ∼99% in a concentration (EC(50) 5.5nM)- and time-dependent manner, without changing Ser(396)-phosphorylated tau level. The insulin-induced increase of tau protein level was abolished by LY294002 [an inhibitor of phosphoinositide 3-kinase (PI3K)] and rapamycin [an inhibitor of mammalian target of rapamycin (mTOR)], but not by PD98059 and U0126 [two inhibitors of mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK)]. Additionally, insulin-induced increase of tau was blocked by cyclohexamide (an inhibitor of protein synthesis), but not by actinomycin D (an inhibitor of gene transcription). Pulse-label followed by polyacrylamide gel electrophoresis revealed that insulin accelerated tau protein synthesis rate (t(1/2)) from 2.6 to 1.9h. Insulin did not change tau mRNA level. Taken together, these results suggest that insulin-induced activation of PI3K∼mTOR pathway up-regulated tau protein via acceleration of protein synthesis, on which insulin promoted neurite-like process outgrowth.

Transcriptional up-regulation of cell surface Na V 1.7 sodium channels by insulin-like growth factor-1 via inhibition of glycogen synthase kinase-3β in adrenal chromaffin cells: enhancement of 22Na+ influx, 45Ca2+ influx and catecholamine secretion

Insulin-like growth factor-1 (IGF-1) plays important roles in the regulation of neuronal development. The electrical activity of Na(+) channels is crucial for the regulation of synaptic formation and maintenance/repair of neuronal circuits. Here, we examined the effects of chronic IGF-1 treatment on cell surface expression and function of Na(+) channels. In cultured bovine adrenal chromaffin cells expressing Na(V)1.7 isoform of voltage-dependent Na(+) channels, chronic IGF-1 treatment increased cell surface [(3)H]saxitoxin binding by 31%, without altering the Kd value. In cells treated with IGF-1, veratridine-induced (22)Na(+) influx, and subsequent (45)Ca(2+) influx and catecholamine secretion were augmented by 35%, 33%, 31%, respectively. Pharmacological properties of Na(+) channels characterized by neurotoxins were similar between nontreated and IGF-1-treated cells. IGF-1-induced up-regulation of [(3)H]saxitoxin binding was prevented by phosphatydil inositol-3 kinase inhibitors (LY204002 or wortmannin), or Akt inhibitor (Akt inhibitor IV). Glycogen synthase kinase-3 (GSK-3) inhibitors (LiCl, valproic acid, SB216763 or SB415286) also increased cell surface [(3)H]saxitoxin binding by ∼ 33%, whereas simultaneous treatment of IGF-1 with GSK-3 inhibitors did not produce additive increasing effect on [(3)H]saxitoxin binding. IGF-1 (100 nM) increased Ser(437)-phosphorylated Akt and Ser(9)-phosphorylated GSK-3β, and inhibited GSK-3β activity. Treatment with IGF-1, LiCl or SB216763 increased protein level of Na(+) channel α-subunit; it was prevented by cycloheximide. Either treatment increased α-subunit mRNA level by ∼ 48% and accelerated α-subunit gene transcription by ∼ 30% without altering α-subunit mRNA stability. Thus, inhibition of GSK-3β caused by IGF-1 up-regulates cell surface expression of functional Na(+) channels via acceleration of α-subunit gene transcription.

Valproic acid antagonizes the capacity of other histone deacetylase inhibitors to activate the Epstein-barr virus lytic cycle

Diverse stimuli reactivate the Epstein-Barr virus (EBV) lytic cycle in Burkitt lymphoma (BL) cells. In HH514-16 BL cells, two histone deacetylase (HDAC) inhibitors, sodium butyrate (NaB) and trichostatin A (TSA), and the DNA methyltransferase inhibitor azacytidine (AzaCdR) promote lytic reactivation. Valproic acid (VPA), which, like NaB, belongs to the short-chain fatty acid class of HDAC inhibitors, fails to induce the EBV lytic cycle in these cells. Nonetheless, VPA behaves as an HDAC inhibitor; it causes hyperacetylation of histone H3 (J. K. Countryman, L. Gradoville, and G. Miller, J. Virol. 82:4706-4719, 2008). Here we show that VPA blocked the induction of EBV early lytic proteins ZEBRA and EA-D in response to NaB, TSA, or AzaCdR. The block in lytic activation occurred prior to the accumulation of BZLF1 transcripts. Reactivation of EBV in Akata cells, in response to anti-IgG, and in Raji cells, in response to tetradecanoyl phorbol acetate (TPA), was also inhibited by VPA. MS-275 and apicidin, representing two additional classes of HDAC inhibitors, and suberoylanilide hydroxamic acid (SAHA) reactivated EBV in HH514-16 cells; this activity was also inhibited by VPA. Although VPA potently blocked the expression of viral lytic-cycle transcripts, it did not generally block the transcription of cellular genes and was not toxic. The levels and kinetics of specific cellular transcripts, such as Stat3, Frmd6, Mad1, Sepp1, c-fos, c-jun, and egr1, which were activated by NaB and TSA, were similar in HH514-16 cells treated with VPA. When combined with NaB or TSA, VPA did not inhibit the activation of these cellular genes. Changes in cellular gene expression in response to VPA, NaB, or TSA were globally similar as assessed by human genome arrays; however, VPA selectively stimulated the expression of some cellular genes, such as MEF2D, YY1, and ZEB1, that could repress the EBV lytic cycle. We describe a novel example of functional antagonism between HDAC inhibitors.

Homologous posttranscriptional regulation of insulin-like growth factor-I receptor level via glycogen synthase kinase-3beta and mammalian target of rapamycin in adrenal chromaffin cells: effect on tau phosphorylation

In cultured bovine adrenal chromaffin cells, approximately 24 h-treatment with insulin-like growth factor-I (IGF-I) decreased cell surface (125)I-IGF-I binding capacity and IGF-I receptor protein level by approximately 64% (EC(50) = 5.0 nM; t(1/2) = approximately 7 h). IGF-I-induced IGF-I receptor decrease was abolished by LY294002 (phosphoinositide 3-kinase inhibitor) and partially attenuated by rapamycin (an inhibitor of mammalian target of rapamycin [mTOR]). SB216763 (an inhibitor of glycogen synthase kinase-3 [GSK-3]) down-regulated IGF-I receptor, which was further decreased by IGF-I. IGF-I increased inhibitory Ser(9)-phosphorylation of GSK-3beta and stimulatory Ser(2448)-phosphorylation of mTOR. l-leucine increased phosphorylation of mTOR (but not GSK-3beta), and down-regulated IGF-I receptor, both events being abolished by rapamycin. IGF-I-induced IGF-I receptor decrease was not prevented by proteolysis inhibitors. Pulse-label with [(35)S]methionine/cysteine followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that SB216763 or L-leucine retarded synthesis of IGF-I receptor and its precursor molecule. SB216763 (but not l-leucine) destabilized IGF-I receptor mRNA and decreased its level, without changing IGF-I receptor gene transcription. In SB216763-treated cells, IGF-I-induced Tyr-autophosphorylation of IGF-I receptor was decreased by 36%, compared to nontreated cells. IGF-I attenuated constitutive Ser(396)-phosphorylation of tau by 30% in nontreated cells, but not in SB216763-treated cells. IGF-I-induced down-regulations of (125)I-IGF-I binding and IGF-I receptor, as well as IGF-I-induced phosphorylations of GSK-3beta and mTOR were restored to the control levels of nontreated cells after washout of IGF-I (10 nM for 12 h)-treated cells. Thus, IGF-I down-regulated functional IGF-I receptor via GSK-3beta inhibition and mTOR activation; constitutive activity of GSK-3beta maintained IGF-I receptor level in nonstimulated cells.

Differential gene expression profiles in embryos of the lizard Podarcis sicula under in ovo exposure to cadmium

Screening for differentially expressed genes is a straightforward approach to study the molecular basis of contaminant toxicity. In this paper, the mRNA differential display technique was applied to analyze transcriptional regulation in response to cadmium exposure in the lizard embryos. Lizard eggs may be particularly susceptible to soil contamination and in ovo exposure may interfere or disrupt normal physiological function in the developing embryo, including regulation of gene expression. Fertilized eggs of the lizard Podarcis sicula were incubated in cadmium-contaminated soil at 25 degrees C for 20 days. Gene expression profiling showed 5 down- and 9 up-regulated genes. Four cDNAs had no homology to known gene sequences, thus suggesting that may either encode not yet identified proteins, or correspond to untranslated regions of mRNA molecules. Four fragments exhibited significant sequence similarity with genes encoding novel proteins or ESTs derived from other vertebrates. The remaining genes are mainly involved in molecular pathways associated with processes such as membrane trafficking, signal transduction, cytoskeletal organization, cell proliferation and differentiation. Cadmium also affected the expression of factors actively involved in the regulation of the transcription machinery. Down-regulated genes are mainly associated with cellular metabolism and cell-cycle regulation and apoptosis. All of these differentially expressed genes may represent candidates that function in cadmium responses. The present study leads to an increased understanding of genes and/or the biochemical pathways involved in perturbation of embryo development following cadmium exposure.

Epigenetic regulation of nervous system development by DNA methylation and histone deacetylation

Alterations in the epigenetic modulation of gene expression have been implicated in several developmental disorders, cancer, and recently, in a variety of mental retardation and complex psychiatric disorders. A great deal of effort is now being focused on why the nervous system may be susceptible to shifts in activity of epigenetic modifiers. The answer may simply be that the mammalian nervous system must first produce the most complex degree of developmental patterning in biology and hardwire cells functionally in place postnatally, while still allowing for significant plasticity in order for the brain to respond to a rapidly changing environment. DNA methylation and histone deacetylation are two major epigenetic modifications that contribute to the stability of gene expression states. Perturbing DNA methylation, or disrupting the downstream response to DNA methylation - methyl-CpG-binding domain proteins (MBDs) and histone deacetylases (HDACs) - by genetic or pharmacological means, has revealed a critical requirement for epigenetic regulation in brain development, learning, and mature nervous system stability, and has identified the first distinct gene sets that are epigenetically regulated within the nervous system. Epigenetically modifying chromatin structure in response to different stimuli appears to be an ideal mechanism to generate continuous cellular diversity and coordinate shifts in gene expression at successive stages of brain development - all the way from deciding which kind of a neuron to generate, through to how many synapses a neuron can support. Here, we review the evidence supporting a role for DNA methylation and histone deacetylation in nervous system development and mature function, and present a basis from which to understand how the clinical use of HDAC inhibitors may impact nervous system function.

Voltage-dependent Na(v)1.7 sodium channels: multiple roles in adrenal chromaffin cells and peripheral nervous system

Voltage-dependent Na+ channels consist of the principal alpha-subunit (approximately 260 kDa), without or with auxiliary beta-subunit (approximately 38 kDa). Nine alpha-subunit isoforms (Na(v)1.1-Na(v)1.9) are encoded in nine different genes (SCN1A-SCN5A and SCN8A-SCN11A). Besides initiating and propagating action potentials in established neuronal circuit, Na+ channels engrave, maintain and repair neuronal network in the brain throughout the life. Adrenal chromaffin cells express Na(v)1.7 encoded in SCN9A, which is widely distributed among peripheral autonomic and sensory ganglia, neuroendocrine cells, as well as prostate cancer cell lines. In chromaffin cells, Na(v)1.7-specific biophysical properties have been characterized; physiological stimulation by acetylcholine produces muscarinic receptor-mediated hyperpolarization followed by nicotinic receptor-mediated depolarization. In human patients with Na(v)1.7 channelopathies, gain-of-pathological function mutants (i.e. erythermalgia and paroxysmal extreme pain disorder) or loss-of-physiological function mutant (channelopathy-associated insensitivity to pain) proved the causal involvement of mutant Na(v)1.7 in generating intolerable pain syndrome, Na(v)1.7 being the first molecular target convincingly identified for pain treatment. Importantly, aberrant upregulation/hyperactivity of even the native Na(v)1.7 produces pain associated with inflammation, nerve injury and diabetic neuropathy in rodents. Various extra- and intracellular signals, as well as therapeutic drugs modulate the activity of Na(v)1.7, and also cause up- and downregulation of Na(v)1.7. Na(v)1.7 seems to play an increasing number of crucial roles in health, disease and therapeutics.

Lysophosphatidic acid-LPA1 receptor-Rho-Rho kinase-induced up-regulation of Nav1.7 sodium channel mRNA and protein in adrenal chromaffin cells: enhancement of 22Na+ influx, 45Ca2+ influx and catecholamine secretion

In cultured bovine adrenal chromaffin cells, chronic (> or = 24 h) treatment with lysophosphatidic acid (LPA) augmented veratridine-induced 22Na+ influx via Na(v)1.7 by approximately 22% (EC(50) = 1 nmol/L), without changing nicotine-induced 22Na+ influx via nicotinic receptor-associated channel. LPA enhanced veratridine (but not nicotine)-induced 45Ca2+ influx via voltage-dependent calcium channel and catecholamine secretion. LPA shifted concentration-response curve of veratridine for 22Na+ influx upward, without altering the EC(50) of veratridine. Ptychodiscus brevis toxin-3 allosterically enhanced veratridine-induced 22Na+ influx by twofold in non-treated and LPA-treated cells. Whole-cell patch-clamp analysis showed that peak Na+ current amplitude was greater by 39% in LPA (100 nmol/L for 36 h)-treated cells; however, I-V curve and steady-state inactivation/activation curves were comparable between non-treated and LPA-treated cells. LPA treatment (> or = 24 h) increased cell surface [3H]saxitoxin binding by approximately 28%, without altering the K(d) value; the increase was prevented by cycloheximide, actinomycin D, or Ki16425, dioctylglycerol pyrophosphate 8:0 (two inhibitors of LPA(1) and LPA3 receptors), or botulinum toxin C3 (Rho inhibitor), Y27632 (Rho kinase inhibitor), consistent with LPA(1) receptor expression in adrenal chromaffin cells. LPA raised Nav1.7 mRNA level by approximately 37%. Thus, LPA-LPA(1) receptor-Rho/Rho kinase pathway up-regulated cell surface Nav1.7 and Nav1.7 mRNA levels, enhancing veratridine-induced Ca2+ influx and catecholamine secretion.

Glycogen synthase kinase-3beta: homologous regulation of cell surface insulin receptor level via controlling insulin receptor mRNA stability in adrenal chromaffin cells

In cultured bovine adrenal chromaffin cells, 48 h-treatment with 20 mmol/L LiCl, 1 mmol/L valproic acid, 30 micromol/L SB216763, 30 micromol/L SB415286, or 100 nmol/L insulin, a condition that inhibits constitutive active glycogen synthase kinase-3 (GSK-3), decreased cell surface (125)I-insulin binding capacity by approximately 39%, without altering the K(d) value; LiCl, SB216763 or insulin decreased insulin receptor (IR) and IR precursor levels, attenuating insulin-induced Tyr-autophosphorylation of IR. LiCl increased inhibitory Ser9-phosphorylation of GSK-3beta at 6 h, decreasing (125)I-insulin binding at 24 h. SB216763-induced (125)I-insulin binding reduction (IC(50) = 3 micromol/L) was preceded by beta-catenin level increase by SB216763 (EC(50) = 11 micromol/L), a hallmark of GSK-3 inhibition. Insulin-induced rapid (> 1 min) Ser9-phosphorylation of GSK-3beta (Nemoto et al. 2006) was followed by approximately 48% decrease of IR level. LiCl did not stimulate endocytosis, nor proteolysis of IR. LiCl destabilized IR mRNA (t(1/2) = 9.3 vs. 6.5 h), decreasing IR mRNA level by approximately 47%, without altering IR gene transcription. Decreases of (125)I-insulin binding and IR level, as well as increased Ser9-phosphorylation of GSK-3beta were restored to the control levels by washing the test compound-treated cells. Thus, GSK-3beta regulates IR level via controlling IR mRNA stability.

Valproate: past, present, and future

Preclinical studies have been carried out during the past four decades to investigate the different mechanisms of action of valproate (VPA). The mechanisms of VPA which seem to be of clinical importance include increased GABAergic activity, reduction in excitatory neurotransmission, and modification of monoamines. These mechanisms are discussed in relation to the various clinical uses of the drug. VPA is widely used as an antiepileptic drug with a broad spectrum of activity. In patients, VPA possesses efficacy in the treatment of various epileptic seizures such as absence, myoclonic, and generalized tonic-clonic seizures. It is also effective in the treatment of partial seizures with or without secondary generalization and acutely in status epilepticus. The pharmacokinetic aspects of VPA and the frequent drug interactions between VPA and other drugs are discussed. The available methods for the determination of VPA in body fluids are briefly evaluated. At present, investigations and clinical trials are carried out and evaluated to explore the new indications for VPA in other conditions such as in psychiatric disorders, migraine and neuropathic pain. Furthermore, the toxicity of VPA, both regarding commonly occurring side effects and potential idiosyncratic reactions are described. Derivatives of VPA with improved efficacy and tolerability are in development.

Destabilization of Na(v)1.7 sodium channel alpha-subunit mRNA by constitutive phosphorylation of extracellular signal-regulated kinase: negative regulation of steady-state level of cell surface functional sodium channels in adrenal chromaffin cells

In cultured bovine adrenal chromaffin cells expressing Na(v)1.7 isoform of voltage-dependent Na(+) channels, treatment (> or = 6 h) with serum deprivation, PD98059, or U0126 increased cell surface [(3)H]saxitoxin ([(3)H]STX) binding by approximately 58% (t(1/2) = 12.5 h), with no change in the K(d) value. Immunoblot analysis showed that either treatment attenuated constitutive phosphorylation of extracellular signal-regulated kinase (ERK) 1 and ERK2 but not of p38 mitogen-activated protein kinase and c-Jun N-terminal kinase (JNK) 1 and JNK2. The increase of [(3)H]STX binding and the attenuated phosphorylation of ERK1 and ERK2 returned to the control nontreated levels after the addition of serum or the washout of PD98059- or U0126-treated cells. Simultaneous treatment of serum deprivation with PD98059 or U0126 did not produce an additional increasing effect on [(3)H]STX binding, compared with either treatment alone. In cells subjected to either treatment, veratridine-induced maximum (22)Na(+) influx was augmented by approximately 47%, with no change in the EC(50) value; Ptychodiscus brevis toxin-3 enhanced veratridine-induced (22)Na(+) influx by 2-fold, as in nontreated cells. Serum deprivation, PD98059, or U0126 increased Na(+) channel alpha- but not beta(1)- subunit mRNA level by approximately 50% between 3 and 24 h; cycloheximide, an inhibitor of protein synthesis, increased alpha-subunit mRNA level and nullified additional increasing effect of either treatment on alpha-subunit mRNA level. Either treatment prolonged half-life of alpha-subunit mRNA from 17.5 to approximately 26.3 h without altering alpha-subunit gene transcription. Thus, constitutively phosphorylated/activated ERK destabilizes Na(+) channel alpha-subunit mRNA via translational event, which negatively regulates steady-state level of alpha-subunit mRNA and cell surface expression of functional Na(+) channels.

Effects of valproic acid, carbamazepine, and phenobarbitone on the fatty acid composition of erythrocyte membranes in children

PURPOSE

To investigate a possible relation between antiepileptic drugs (AEDs) and the fatty acid composition of membranes.

METHODS

Fatty acid (FA) composition of erythrocytes was studied in children with epilepsy receiving AED monotherapy. Children taking valproate (VPA, n = 28), carbamazepine (CBZ, n = 17), or phenobarbitone (PB, n = 14) were compared with healthy controls (n = 25). FAs were measured by capillary-gas chromatography (GC-FID).

RESULTS

Significant changes (p < 0.05) in the FA composition of membranes were found. In children treated with VPA, C13:0 was decreased (8.2 +/- 2% vs. 10.7 +/- 4% in controls) and C14:0 increased (1.4 +/- 0.5% vs.1 +/- 0.5% in controls). C17:0 again was reduced (9.9 +/- 4% vs. 13.2 +/- 6% in controls), whereas the long-chained acids were enhanced: C18:2n-6 (6 +/- 2.4% vs. 3.9 +/- 2.5% in controls), and C20:4n-6 (1.9 +/- 1.7% vs. 1.4 +/- 0.5% in controls). The nonidentified FAs also increased with VPA therapy: 2.5 +/- 0.8% versus 1.7 +/- 0.9% in controls. Children treated with CBZ showed only minimal changes of FA composition: C13:0 was decreased compared with controls (8 +/- 2% vs. 10.7 +/- 4%). No changes were seen in patients taking PB. The mean corpuscular volume (MCV) showed important differences between the study groups: MCV was 84.7 +/- 6.0 fl during VPA therapy (p < 0.001) and 85.7 +/- 4.1 fl with CBZ (p < 0.001). During PB, the MCV increased to 82.87 +/- 3.29 fl compared with controls (78.73 +/- 4.92 fl; p < 0.01).

CONCLUSIONS

VPA therapy is associated with changes of the FA composition of membranes, which is not the case with PB therapy. The implications of this finding remain to be established.

Differential effects of bupivacaine enantiomers, ropivacaine and lidocaine on up-regulation of cell surface voltage-dependent sodium channels in adrenal chromaffin cells

In cultured bovine adrenal chromaffin cells, (+/-)-bupivacaine inhibited veratridine-induced 22Na(+) influx (IC(50) 6.8 microM). The IC(50) of (+)-bupivacaine (2.8 microM) was 6.2-, 7.4-, and 17.1-fold lower than those of (-)-bupivacaine (17.3 microM), (-)-ropivacaine (20.6 microM), and lidocaine (47.8 microM). Chronic (i.e. 3-h) treatment of cells with (+/-)-bupivacaine increased cell surface [3H]saxitoxin ([3H]STX) binding capacity by 48% (EC(50) of 233 microM; t(1/2)=7.4 h), without changing the K(d) value. Treatment for 24 h with either (+)- or (-)-bupivacaine, or (-)-ropivacaine elevated [3H]STX binding, whereas 24-h treatment with lidocaine had no effect. The rise of [3H]STX binding by (+/-)-bupivacaine was prevented by cycloheximide, an inhibitor of protein synthesis, or brefeldin A, an inhibitor of cell surface vesicular exit from the trans-Golgi network; however, (+/-)-bupivacaine did not increase Na(+) channel alpha- and beta(1)-subunit mRNA levels. In cells subjected to (+/-)-bupivacaine treatment (1 mM for 24 h) followed by 3-h washout, veratridine-induced 22Na(+) influx was enhanced, even when measured in the presence of ouabain, an inhibitor of Na(+),K(+)-ATPase. Ptychodiscus brevis toxin-3 potentiated veratridine-induced 22Na(+) influx by 2.3-fold in the (+/-)-bupivacaine-treated cells, as in non-treated cells. These results suggest that lipophilic bupivacaine enantiomers or (-)-ropivacaine acutely inhibit Na(+) channel gating, whereas its chronic treatment up-regulates cell surface expression of Na(+) channels via translational and externalization events.

Mood stabilizers in Alzheimer's disease: symptomatic and neuroprotective rationales

OBJECTIVE

This paper provides a case study of 'reverse translational research', in which empirical clinical trials focused on relieving psychopathological symptoms of Alzheimer's disease (AD) ultimately led to mechanism-based trials addressing aspects of the underlying pathophysiology of Alzheimer's disease. AD is multi-dimensional in nature, characterized not only by cognitive and functional decline but by neuropsychiatric symptoms that develop commonly and are associated with considerable morbidity. There have been a large number of empirical trials of various pharmacological agents to reduce these symptoms, such as agitation. Although antipsychotics are used most frequently for agitation, the usual effect size is modest, and there is a range of tolerability and/or safety issues, leading to the hope that alternatives can be found. Furthermore, most clinical trials addressing psychopathology have not been mechanism-based and none have attempted an alternative approach, namely, to delay or prevent the emergence of psychopathology.

FINDINGS

The evidence of clinical trials is reviewed regarding the safety, tolerability, and apparent efficacy of the mood stabilizers carbamazepine and valproate for agitation associated with AD. Possible mechanisms of action of valproate are reviewed, leading to the surprising conclusion that neuroprotective properties may account for some of its clinical effects. These mechanisms (including activation of wnt-dependent signaling and upregulation of bcl-2, among others) may be particularly relevant for long-term treatment of AD.

CONCLUSIONS

These clinical and mechanistic findings were combined in the development of a novel clinical trial examining whether chronic valproate therapy can attenuate the clinical progression of AD, which will be implemented by the Alzheimer's Disease Cooperative Study. The design addresses valproate's potential to delay or prevent the onset of agitation in patients lacking agitation to begin with, as well as to slow progressive decline in cognition and daily functioning.

Voltage-gated sodium channels in epilepsy

Animal experiments, and particularly functional investigations on human chronically epileptic tissue as well as genetic studies in epilepsy patients and their families strongly suggest that some forms of epilepsy may share a pathogenetic mechanism: an alteration of voltage-gated sodium channels. This review summarizes recent data on changes of sodium channel expression, molecular structure and function associated with epilepsy, as well as on the interaction of new and established antiepileptic drugs with sodium currents. Although it remains to be determined precisely how and to what extent altered sodium-channel functions play a role in different epilepsy syndromes, future promising therapy approaches may include drugs modulating sodium currents, and particularly substances changing their inactivation characteristics.

Differential effects of short and prolonged exposure to carvedilol on voltage-dependent Na(+) channels in cultured bovine adrenal medullary cells

We examined the effects of short and prolonged exposure to carvedilol, an antihypertensive and beta-adrenoceptor blocking drug, on voltage-dependent Na(+) channels in cultured bovine adrenal medullary cells. Carvedilol (1-100 microM) reduced (22)Na(+) influx induced by veratridine, an activator of voltage-dependent Na(+) channels. Carvedilol also suppressed veratridine-induced (45)Ca(2+) influx and catecholamine secretion in a concentration-dependent manner similar to that of (22)Na(+) influx. Prolonged exposure of the cells to 10 microM carvedilol increased [(3)H]saxitoxin ([(3)H]STX) binding, which reached a plateau at 12 h and was still observed at 48 to 72 h. Scatchard analysis of [(3)H]STX binding revealed that carvedilol increased the B(max) value (control, 14.9 +/- 0.9 fmol/10(6) cells; carvedilol, 23.8 +/- 1.2 fmol/10(6) cells) (n = 3, P < 0.05) without altering the K(d) value, suggesting a rise in the number of cell surface Na(+) channels. The increase in [(3)H]STX binding by carvedilol was prevented by cycloheximide, an inhibitor of protein synthesis, whereas carvedilol changed neither alpha- nor beta(1)-subunit mRNA levels of Na(+) channels. The carvedilol-induced increase of [(3)H]STX binding was abolished by brefeldin A and H-89, inhibitors of intracellular vesicular trafficking of proteins from the trans-Golgi network and of cyclic AMP-dependent protein kinase (protein kinase A), respectively. The present findings suggest that short-term treatment with carvedilol reduces the activity of Na(+) channels, whereas prolonged exposure to carvedilol up-regulates cell surface Na(+) channels. This may add new pharmacological effects of carvedilol to our understanding in the treatment of heart failure and hypertension.

Selective inhibition of nicotinic cholinergic receptors by proadrenomedullin N-terminal 12 peptide in bovine adrenal chromaffin cells

We studied whether a novel proadrenomedullin derived peptide was present and what was its physiological function in cultured bovine adrenal chromaffin cells. We found a high level of proadrenomedullin N-terminal 12 peptide (PAMP-12) which consists of a peptide from 9th amino acid to 20th amino acid of proadrenomedullin N-terminal 20 peptide (PAMP-20). PAMP-12 was released from the cells along with catecholamine upon stimulation of nicotinic cholinergic receptors. When PAMP-12 was added in the incubation medium, this peptide inhibited nicotinic receptor-mediated catecholamine release and influx of Na(+) and Ca(2+) into the cells. PAMP-12 did not affect catecholamine release evoked by histamine or by depolarization by high concentration of potassium. PAMP-12 also inhibited synthesis of catecholamines as well as the activation of tyrosine hydroxylase by nicotinic stimulation. Thus, PAMP-12 is an endogenous peptide that regulates release and synthesis of catecholamines by acting on nicotinic cholinergic receptors in an autocrine manner in adrenal chromaffin cells.

Comorbid bipolar disorder in Tourette's syndrome responds to the nicotinic receptor antagonist mecamylamine (Inversine)

BACKGROUND

We have previously proposed that the therapeutic effect of transdermal nicotine in Tourette's syndrome may involve nicotinic receptor inactivation resulting from a prolonged continuous exposure to nicotine. In vitro studies with nicotine and preliminary positive experience with mecamylamine (Inversine), a nicotinic receptor antagonist, in the clinical treatment of Tourette's syndrome patients, further supports the receptor inactivation hypothesis.

METHODS

We retrospectively documented an unexpected therapeutic response to mecamylamine (2.5-7.5 mg/day) in two Tourette's syndrome patients who were subsequently found to have comorbid bipolar disorder as defined by DSM-IV criteria.

RESULTS

In patient 1, the mood-stabilizing effect of mecamylamine was noticed by the patient during the course of mecamylamine treatment and brought to our attention, whereas for patient 2, manic symptoms were only apparent clinically following cessation of mecamylamine treatment.

CONCLUSIONS

The clinical observations presented here suggest that nicotinic antagonists might be potential therapeutic agents for the treatment of bipolar disorder. Double-blind, placebo-controlled studies are now necessary to investigate these observations under more rigorous conditions.

Short- and long-term differential effects of neuroprotective drug NS-7 on voltage-dependent sodium channels in adrenal chromaffin cells

In cultured bovine adrenal chromaffin cells, NS-7 [4-(4-fluorophenyl)-2-methyl-6-(5-piperidinopentyloxy) pyrimidine hydrochloride], a newly-synthesized neuroprotective drug, inhibited veratridine-induced (22)Na(+) influx via voltage-dependent Na(+) channels (IC(50)=11.4 microM). The inhibition by NS-7 occurred in the presence of ouabain, an inhibitor of Na(+),K(+) ATPase, but disappeared at higher concentration of veratridine, and upon the washout of NS-7. NS-7 attenuated veratridine-induced (45)Ca(2+) influx via voltage-dependent Ca(2+) channels (IC(50)=20.0 microM) and catecholamine secretion (IC(50)=25.8 microM). Chronic (>/=12 h) treatment of cells with NS-7 increased cell surface [(3)H]-STX binding by 86% (EC(50)=10.5 microM; t(1/2)=27 h), but did not alter the K(D) value; it was prevented by cycloheximide, an inhibitor of protein synthesis, or brefeldin A, an inhibitor of vesicular transport from the trans-Golgi network, but was not associated with increased levels of Na(+) channel alpha- and beta(1)-subunit mRNAs. In cells subjected to chronic NS-7 treatment, (22)Na(+) influx caused by veratridine (site 2 toxin), alpha-scorpion venom (site 3 toxin) or beta-scorpion venom (site 4 toxin) was suppressed even after the extensive washout of NS-7, and veratridine-induced (22)Na(+) influx remained depressed even at higher concentration of veratridine; however, either alpha- or beta-scorpion venom, or Ptychodiscus brevis toxin-3 (site 5 toxin) enhanced veratridine-induced (22)Na(+) influx as in nontreated cells. These results suggest that in the acute treatment, NS-7 binds to the site 2 and reversibly inhibits Na(+) channels, thereby reducing Ca(2+) channel gating and catecholamine secretion. Chronic treatment with NS-7 up-regulates cell surface Na(+) channels via translational and externalization events, but persistently inhibits Na(+) channel gating without impairing the cooperative interaction between the functional domains of Na(+) channels.

Chronic valproate treatment increases expression of endoplasmic reticulum stress proteins in the rat cerebral cortex and hippocampus

BACKGROUND

Sodium valproate is a highly effective treatment for bipolar disorder, but its mechanism of action remains poorly understood. We recently found with differential display polymerase chain reaction that valproate regulates the expression of the endoplasmic reticulum stress protein GRP78 in the rat cerebral cortex. In our study, we investigated the effect of this drug on the other members of the endoplasmic reticulum stress protein family, GRP94 and calreticulin, and we studied the brain regional distribution of GRP78, GRP94, and calreticulin.

METHODS

Immunohistochemistry was used to measure protein levels of GRP78, GRP94, and calreticulin after treatment with sodium valproate (300 mg/kg, intraperitoneal) in specific rat brain regions.

RESULTS

We report here that chronic treatment with valproate also increased expression of other members of the endoplasmic reticulum stress protein family, such as GRP94 and calreticulin. The brain regional distribution of these changes was similar for all three proteins, with marked increase detected in the frontal cortex, parietal cortex, and CA1 region of the hippocampus.

CONCLUSIONS

Because GRP78, GRP94, and calreticulin possess molecular chaperone activity and bind Ca(2+) in the endoplasmic reticulum, the pharmacologic action of valproate may involve one or more of these processes.

Inhibition by neuroprotective drug NS-7 of nicotine-induced 22Na(+) influx, 45Ca(2+) influx and catecholamine secretion in adrenal chromaffin cells

In cultured bovine adrenal chromaffin cells, NS-7 [4-(4-fluorophenyl)-2-methyl-6-(5-piperidinopentyloxy) pyrimidine hydrochloride], a newly-synthesized neuroprotective drug, inhibited nicotine-induced 22Na(+) influx via nicotinic receptors (IC(50)=15.5 microM); the suppression by NS-7 was observed in the presence of ouabain, an inhibitor of Na(+),K(+)-ATPase, and was not attenuated upon the washout of NS-7. NS-7 decreased nicotine-induced maximum influx of 22Na(+) without altering the EC(50) value of nicotine. Also, NS-7 diminished nicotine-induced 45Ca(2+) influx via nicotinic receptors and voltage-dependent Ca(2+) channels (IC(50)=14.1 microM) and catecholamine secretion (IC(50)=19.5 microM). These results suggest that NS-7 produces noncompetitive and long-lasting inhibitory effects on neuronal nicotinic receptors in adrenal chromaffin cells, and interferes with the stimulus-secretion coupling.

Protein kinase C-alpha and -epsilon down-regulate cell surface sodium channels via differential mechanisms in adrenal chromaffin cells

In cultured bovine adrenal chromaffin cells, our [3H]saxitoxin ([3H]STX) binding, immunoblot, and northern blot analyses specified protein kinase C (PKC) isoform-specific posttranscriptional and posttranslational mechanisms that direct down-regulation of cell surface Na channels. Immunoblot analysis showed that among 11 PKC isoforms, adrenal chromaffin cells contained only conventional (c)PKC-alpha, novel (n)PKC-epsilon, and atypical (a)PKC-zeta. Treatment of adrenal chromaffin cells with 100 nM 12-O-tetradecanoylphorbol 13-acetate (TPA) or 100 nM phorbol 12,13-dibutyrate (PDBu) caused a rapid (<15 min) and sustained (>15 h) translocation of PKC-alpha and -epsilon (but not -zeta) from cytosol to membranes, whereas a biologically inactive 4alpha-TPA had no effect. Thymeleatoxin (TMX), an activator of cPKC, produced similar membrane association of only PKC-alpha at 100 nM, with the potency of TMX being comparable with those of TPA and PDBu. Treatment with either 100 nM TPA or 100 nM TMX reduced cell surface [3H]STX binding to a comparable extent at 3, 6, and 12 h, whereas TPA lowered the binding to a greater extent than TMX at 15, 18, and 24 h; at 15 h, Gö6976, a specific inhibitor of cPKC, completely blocked TMX-induced decrease of [3H]STX binding while preventing by merely 57% TPA-induced decrease of [3H]STX binding. Treatment with 100 nM TPA lowered the Na channel alpha-subunit mRNA level between 3 and 12 h, with its maximum 52% fall at 6 h, and it was accompanied by a subsequent 61 % rise of the beta1-subunit mRNA level at 24 h. Gö6976 failed to prevent TPA-induced reduction of the alpha-subunit mRNA level; TMX did not change the alpha- and beta1-subunit mRNA levels throughout the 24-h treatment. Brefeldin A, an inhibitor of vesicular exit from the trans-Golgi network, augmented TPA- and TMX-induced decrease of [3H]STX binding at 1 and 3 h. Our previous and present studies suggest that PKC down-regulates cell surface Na channels without altering the allosteric gating of Na channels via PKC isoform-specific mechanisms; cPKC-alpha promotes Na channel internalization, whereas nPKC-epsilon decreases the alpha-subunit mRNA level by shortening the half-life of alpha-subunit mRNA without changing its gene transcription.

Protein kinase C and the opposite regulation of sodium channel alpha- and beta1-subunit mRNA levels in adrenal chromaffin cells

Our previous [3H]saxitoxin binding and 22Na influx assays showed that treatment of cultured bovine adrenal chromaffin cells with 12-O-tetradecanoylphorbol 13-acetate (TPA) or phorbol 12,13-dibutyrate (PDBu), an activator of protein kinase C (PKC), decreased the number of cell surface Na channels (IC50 = 19 nM) but did not alter their pharmacological properties; Na channel down-regulation developed within 3 h, reached the peak decrease of 53% at 15 h, and was mediated by transcriptional/translational events. In the present study, treatment with 100 nM TPA lowered the Na channel alpha-subunit mRNA level by 34 and 52% at 3 and 6 h, followed by restoration to the pretreatment level at 24 h, whereas 100 nM TPA elevated the Na channel beta1-subunit mRNA level by 13-61% between 12 and 48 h. Reduction of alpha-subunit mRNA level by TPA was concentration-dependent (IC50 = 18 nM) and was mimicked by PDBu but not by the biologically inactive 4alpha-TPA; it was prevented by H-7, an inhibitor of PKC, but not by HA-1004, a less active analogue of H7, or by H-89, an inhibitor of cyclic AMP-dependent protein kinase. Treatment with cycloheximide, an inhibitor of protein synthesis, per se sustainingly increased the alpha-subunit mRNA level and decreased the beta1-subunit mRNA level for 24 h; also, the TPA-induced decrease of alpha-subunit mRNA and increase of beta1-subunit mRNA were both totally prevented for 24 h by concurrent treatment with cycloheximide. Nuclear run-on assay showed that TPA treatment did not alter the transcriptional rate of the alpha-subunit gene. A stability study using actinomycin D, an inhibitor of RNA synthesis, revealed that TPA treatment shortened the t(1/2) of alpha-subunit mRNA from 18.8 to 3.7 h. These results suggest that Na channel alpha- and beta-subunit mRNA levels are differentially down- and up-regulated via PKC; the process may be mediated via an induction of as yet unidentified short-lived protein(s), which may culminate in the destabilization of alpha-subunit mRNA without altering alpha-subunit gene transcription.

Lithium and valproate differentially regulate brain regional expression of phosphorylated CREB and c-Fos

Previous studies in our laboratory have shown that the mood stabilizers, lithium and valproate (VPA), regulate the transcription factors, cyclic AMP responsive element binding protein (CREB), c-Fos and c-Jun, differentially in cultured human neuroblastoma SH-SY5Y cells. Here, we confirm these findings in rat brain and further study the brain-regional effects of these drugs using immunohistochemistry. We found that although chronic treatment with LiCl or VPA did not change the expression of c-Fos and c-Jun, acute treatment with either drugs increased c-Fos expression but not c-Jun expression in CA1 and CA3 regions of hippocampus. Chronic treatment with LiCl, but not VPA, decreased CREB phosphorylation in rat cerebral cortex and hippocampus. These results suggest that lithium and VPA may act on different pathways to bring about their long-term prophylactic effects on bipolar disorder (BD). The regulation of CREB phosphorylation may be relevant to lithium effect. VPA, which is also effective in BD, may be linked to other pathways.